(a) Field of the Invention
The present invention relates to an economical method of removing nitrogen and producing a large quantity of struvite from nitrogen-rich wastewater.
(b) Description of the Related Art
There are many existing biological and physical-chemical methods for removing phosphorus and nitrogen and these methods have drawbacks such as difficulties in maintaining the removal efficiency while being costly as well. Recently, the research of simultaneous removal of nitrogen and phosphorus through production of struvite (magnesium ammonium phosphate, MAP) has been actively pursued. Pure MAP is composed of magnesium ion, ammonium nitrogen, and phosphate in a mole ratio of 1:1:1, reciprocally. The reaction formula is:Mg2++NH4++PO43−+6H2O→MgNH4PO46H2O
Additionally, MAP analogs such as Calcium Ammonium Phosphate, in which magnesium ion is substituted by calcium ion, may be produced and MAP and MAP analogs are called as struvite. Removal of phosphorus and nitrogen from wastewater by the form of struvite can effectively eliminate phosphorus and nitrogen simultaneously and struvite is a slow-release fertilizer that is non-toxic and has a lasting effect without being easily oxidized over a long period of usage.
The technologies of struvite formation include:                Tsunekawa et al., Abstracts of Japanese Patent No. 11-267665        Trentelman, U.S. Pat. No. 4,389,317        Korea Patent No. 2002-0005521        Korea Patent No. 2000-0019613        Korea Patent No. 2004-0070408        Korea Patent No. 2007-0135309        
However, in the instance of these previous methods, a considerable amount of expenses are required for supplementing magnesium, calcium and phosphorus chemicals when treating nitrogen-rich wastewater with a low concentration of magnesium, calcium, and phosphorus ions. As a result, struvite production is limited and a large quantity of ammonium nitrogen remains. There is yet to be a technique that is prepared to compensate such short comings. In other words, there is not a technique or patent that cost-efficiently supplies magnesium, calcium, and phosphorus ions in order to additionally remove nitrogen from nitrogen-rich wastewater while economically increasing struvite production.